FACULTY OF AGRICULTURAL SCIENCES
FACULTY OF AGRICULTURAL SCIENCES AND ALLIED INDUSTRIES
FACULTY OF AGRICULTURAL SCIENCES
AND ALLIED INDUSTRIES
MULTIPLE FACTOR HYPOTHESIS
Polygenic inheritance quantitative characters
It shows more or less continous variation and are governed by a large number of genes called ' multiple gene' or 'multiple factor' or 'polymeric genes' or 'polygenes'.
Nilson -Ehle's studies on kernel colour in wheat The Swedish geneticist Nilson
different true breeding strains of wheat with red kernels and those with white kernels.
Careful examinations however revealed that, a red colour of the F1 was not so intense as the red colour of the parent and that in the
dark as those of parent and others only as dark as those of the F1. It was possible to separate the F2 in to the following;
Dark red
Meidum dark red Medium red Light red White
Red Parents R1 R1
F1 R1 r1
F2 1
It is evident that, red colour is due to two pairs of alleles. Each gene is capable of producing red colour. Each is in completely dominant over white and in cumulative in its effect. The intensity of red colour depends upon the number of colour producing gene present.
From these studies, Nilson
the inheritance of quantitative characters. This assumes that there is a series of independent genes for a given quantitative trait. Dominance is usually in complete, but these genes are cumulative or additive in their effect. Each gene adds
UNIT 3- FUNDAMENTALS OF GENETICS (GPB
MULTIPLE FACTOR HYPOTHESIS
Polygenic inheritance quantitative characters
It shows more or less continous variation and are governed by a large number of genes called ' multiple gene' or 'multiple factor' or 'polymeric genes' or
Ehle's studies on kernel colour in wheat
The Swedish geneticist Nilson - Ehle (1908) effected crosses between different true breeding strains of wheat with red kernels and those with white kernels.
Careful examinations however revealed that, a red colour of the F1 was not so intense as the red colour of the parent and that in the F2. Some red grains wree as dark as those of parent and others only as dark as those of the F1. It was possible to separate the F2 in to the following;
1 - R1 R2 R2 R2 - 4 contributing genes.
4 - 3 contributing genes 6 - "
4 - "
1 - No "
White
R2 R2 x r1 r1 r2 r2
R2 r2 Medium red.
: 4 : 6 : 4
It is evident that, red colour is due to two pairs of alleles. Each gene is capable of producing red colour. Each is in completely dominant over white and in cumulative in its effect. The intensity of red colour depends upon the number of colour producing gene present.
From these studies, Nilson-Ehle proposed the multiple factor
the inheritance of quantitative characters. This assumes that there is a series of independent genes for a given quantitative trait. Dominance is usually in complete, but these genes are cumulative or additive in their effect. Each gene adds
FUNDAMENTALS OF GENETICS (GPB-121)
It shows more or less continous variation and are governed by a large number of genes called ' multiple gene' or 'multiple factor' or 'polymeric genes' or
(1908) effected crosses between different true breeding strains of wheat with red kernels and those with white kernels.
Careful examinations however revealed that, a red colour of the F1 was not so F2. Some red grains wree as dark as those of parent and others only as dark as those of the F1. It was possible
4 contributing genes.
r1 r1 r2 r2
: 1
It is evident that, red colour is due to two pairs of alleles. Each gene is capable of producing red colour. Each is in completely dominant over white and in cumulative in its effect. The intensity of red colour depends upon the number of
Ehle proposed the multiple factor hypothesis for the inheritance of quantitative characters. This assumes that there is a series of independent genes for a given quantitative trait. Dominance is usually in complete, but these genes are cumulative or additive in their effect. Each gene adds something
121)
to the strength of expression of the character, whereas its allele does not posses any effect.
Transgressive segregation
The appearance of individuals in the F2 or a subsequent generation which exceed the parental limits withrespect to one or more characters.
e.g. Skin colour in human beings White x Negro Mariages -
By Daven port (1913) by multiple factor hypothesis.
Hypothetical example,
Plant height (cm)
200 cm tall 100 cm tall
T1 T1 T2 T2 x t1 t1 t2 t2
F1 T1 t1 T2 t2 150 cm T1 T2 - Active contributing genes
T1 t2 neutral or inert alleles F2 1 : 4 : 6 : 4 : 1 Cm 200 175 150 125 100 cm.
Fine structure of Gene
Benzer in 1955 divided the gene in to recon, muton and cistron. He worked on rII locus of baceriophage. Recon is the recombinational unit, muton is the mutational
unit and cistron is the functional unit.
